Views: 0 Author: Site Editor Publish Time: 2025-11-18 Origin: Site
For the vast majority of 2K overmolding applications, the ideal soft material thickness falls between 0.8 mm and 2.0 mm.
Within this range, there is a particularly reliable and commonly used sweet spot:
1.2 mm to 1.5 mm
This range consistently provides the best balance of bond strength, manufacturability, cost, and final product feel.
The overmolding process is more than just injecting one material onto another. It's about creating a robust, molecular-level bond. The thickness of the soft layer directly impacts this in three key ways:
Thermal Bonding: The molten TPE/TPU must be hot enough to slightly melt the surface of the rigid substrate, creating a thin layer where the materials interdiffuse and fuse together. A layer that is too thin cools too quickly, preventing this fusion.
Flow and Pressure: The soft material must flow easily and completely into the mold cavity. Thickness affects flow resistance; too thin, and the material can't fill the space, leading to short shots.
Shrinkage and Stress: Soft materials (especially TPE-S) have high shrinkage rates. An excessively thick section will cool unevenly, pulling inward and creating visible sink marks on the surface.
The choice of materials is the single biggest factor determining your ideal wall thickness. Here’s a breakdown of common combinations:
The Classic Combo: This is the most widespread partnership in consumer electronics, tools, and household items.
Material Behavior: TPE-S offers a soft feel but has high shrinkage. PC/ABS bonds chemically very well with TPE-S.
Recommended Thickness: 1.2 mm - 1.8 mm
Reasoning: This range provides enough material volume to maintain heat for a strong bond while keeping shrinkage-induced defects to a minimum. The 1.5mm mark is often the perfect target.
The Tough Duo: TPU is known for its excellent abrasion resistance, toughness, and high grip, but it has high melt viscosity.
Material Behavior: TPU flows less easily than TPE-S. Its chemical affinity with PC/ABS is excellent.
Recommended Thickness: 1.5 mm - 2.2 mm
Reasoning: The thickness needs to be on the higher side to reduce flow resistance and allow the viscous TPU to fill the cavity completely without requiring excessive injection pressure.
The Challenging Partnership: Polypropylene (PP) is a low-surface-energy plastic, meaning it's notoriously difficult for most materials to bond to chemically.
Material Behavior: TPV is specifically formulated to bond with PP. The bond relies heavily on mechanical interlocking (using undercuts and grooves in the mold design) rather than pure chemical fusion.
Recommended Thickness: 1.8 mm - 2.5 mm
Reasoning: A thicker layer ensures there is enough material to flow into and encapsulate the mechanical locking features on the PP substrate, creating a strong physical anchor.
The Premium Option: Used in high-end medical, culinary, and baby care products for its ultra-soft feel and inertness.
Material Behavior: LSR has very low viscosity (it flows easily) and minimal shrinkage. Chemical bonding is poor, so mechanical interlocking is essential.
Recommended Thickness: 1.5 mm - 3.0+ mm
Reasoning: Thickness is less about process and more about function and feel. Designers can specify thicker layers for a luxurious, squishy grip without worrying about sink marks.
Prioritize Uniformity: Aim for a consistent wall thickness throughout the design. Use smooth radii to transition between different thicknesses to prevent flow lines and stress concentration.
Design for Mechanical Interlock: Never rely solely on chemical adhesion. Always include undercuts, grooves, through-holes, and textured surfaces on the rigid substrate. This is absolutely critical for difficult materials like PP.
Consult Your Material Supplier: This is the most important step. The supplier of your TPE, TPU, or LSR can provide the exact shrinkage rate and give a data-backed recommendation for your specific material grade and application.
Prototype and Test: Before cutting steel, create prototypes using 3D printing or soft tooling to validate the grip, feel, and bond strength of your chosen thickness.
While 1.2 mm to 1.5 mm is the universal starting point for 2K overmolding, the final decision must be a conversation between your design intent and your material choice.
For easy-bonding pairs like TPE on PC/ABS, stay in the sweet spot.
For viscous materials like TPU, go thicker for flow.
For difficult substrates like PP, go thicker for mechanical locking.
For premium feel with LSR, let function dictate thickness.
By understanding the "why" behind the numbers, you can confidently design 2K overmolded parts that are not only beautiful and functional but also manufacturable and reliable. Start with the golden range, then refine based on your material marriage.
